1. Field of the Invention
The field of the invention relates to the control of aquatic weeds in canals, rivers, ponds, lakes and impoundments.
2. Description of the Prior Art
The problems of controlling the growth of organisms in aqueous systems are serious and growing daily more severe. Submerged aquatic weeds, for example, cause major problems in irrigation and water distribution systems. The growth of weeds in irrigation canals greatly reduces the conductivity and capacity of such systems, with resulting substantial economic loss. Large sums are therefore currently being spent in the mechanical and other methods of removal of weed growths from irrigation canals, especially in the southern and western parts of the United States.
Because of the great difficulties involved in the mechanical removal of weeds and other undesired forms of aquatic life from irrigation canals, ponds, lakes, impoundments, etc., it has been proposed to utilize chemical control. Accordingly, various types of chemicals have been added to such bodies of water.
In the prior art, British Pat. No. 1,290,223, teaches the use of some thiadiazolylureas substituted in the 5-position of the thiadiazole ring with alkenylthio, alkynylthio, and other substituted thio substituents. The compounds are alleged to be growth regulators and terrestrial herbicides. There is no teaching that the compounds are useful against aquatic weeds and none of the tests described in the document suggest the compounds would be active as aquatic herbicides. In addition, the compounds are structurally different from those included within the scope of the instant application.
Also in the prior art is South African Pat. No. 70/04928 (published July 19, 1971), which teaches thiadiazolyl-(2)-ureas as terrestrial herbicides for the control of monocotyledonous and dicotylendonous weeds and wild grasses. The compounds are alleged to be useful in controlling leguminous weeds, umbelliferous plants, millet, mustard, goosefoot, slender foxtail, and chamomile without damage to crops such as grain. There is no teaching that the compounds would be useful as aquatic herbicides.
In addition, British Pat. No. 1,282,308, is directed to 5-mercapto-1,3,4-thiadiazol-2-ylureas alleged to be herbicidal and useful for pre- or postemergence control of mono- and dicotyledonous weeds. There is no teaching in this patent that the disclosed compounds would be useful as aquatic herbicides.
Further, Offenlegungsschrift No. 2,028,778 (Dec. 23, 1971), discloses thiadiazolylurea herbicides 5-substituted by sulfinyl or sulfonyl groups. These compounds are alleged to be soil and leaf herbicides active against mono- and dicotyledonous weeds pre- and postemergence. The activity is alleged to be selective at rates of 0.5-1 kg./ha. and total at rates of 2-10 kg./ha. There is no teaching that the compounds would be active as aquatic herbicides.
Also in the prior art, Canadian Pat. No. 942751 is directed to 5-alkylsulfinyl or sulfonyl 1,3,4-thiadiazolylureas useful as terrestrial herbicides. The compounds included in this patent are alleged to be total herbicides when applied at rates of 2-10 kg./ha., as well as being active for weeds propagated by seeds when applied at rates of 0.25-1 kg./ha. There is no teaching that the compounds would be useful as aquatic herbicides.
In addition, East German Pat. No. 85,222 (Oct. 12, 1971), teaches 2-ureido-1,3,4-thiadiazoles having herbicidal activity. The compounds are taught as being suitable for general weed control as soil sterilants, as plant growth regulators, for treating the foliage of weeds, for the desiccation of defoliation of crop plants, and as selective terrestrial herbicides (pre- and postemergence), being allegedly particularly useful for selectively combatting weeds in sugar beet and potato cultures, for instance. The compounds are taught as being active against both annual and perennial broadleaved and grassy weeds with the rate of application generally 0.5-5 kg./ha. Again, there is no teaching that the compounds would have utility as aquatic herbicides.
Also in the prior art is Rathgeb et al., U.S. Pat. No. 3,929,816 (Dec. 30, 1975), which discloses 1,3,4-thiadiazolyl-(2)-ureas substituted on the 5-position of the thiadiazole ring with an aliphatic thio or cycloaliphatic thio grouping, the aliphatic or cycloaliphatic moiety being a saturated or unsaturated hydrocarbon radical having at most six carbon atoms, and which may be unsubstituted or substituted by halogen or lower alkoxy. The compounds are alleged to be useful as herbicides for the control of mono- and dicotyl weeds and wild grasses. Only terrestrial plants are alleged to be controlled by the compounds. There is no suggestion the compounds disclosed by this reference would be active as aquatic herbicides.
Another reference in the prior art is Kubo et al., J. Ag. Food Chem. 18, 60-65 (1970), which discloses a number of 1,3,4-thiadiazole derivatives alleged to possess herbicidal properties. The compounds of this reference lack the alkyl derivative on the urea nitrogen atom directly attached to the thiadiazole nucleus, and thus the Kubo et al. compounds are outside the generic scope of the compounds of the instant application. Kubo et al. evaluated their compounds by preemergence, postemergence, and irrigated water treatment methods. The irrigated water method was utilized by Kubo et al. in testing the herbicidal activity of their compounds against barnyardgrass, slender spikerush and rice. None of the Kubo et al. 5-(substituted thio) compounds were herbicidal to slender spikerush or rice in the irrigated water method.
Another reference is Belgian Pat. No. 820,724, also identified by Derwent No. 27434W, which reference discloses allegedly new 5-alkylsulfonyl- and 5-alkylsulfinyl-1,3,4-thiadiazolylureas, said to be useful as selective pre- or postemergence herbicides for controlling grasses and broadleaf weeds in groundnuts, potatoes, peas, maize and sorghum. The compounds are thus taught for use as terrestrial herbicides. There is no teaching in the reference that such compounds would be useful as aquatic herbicides.
Yet another reference is German Offenlegungsschrift No. 2407144, also identified by Derwent No. 60587W, which reference discloses herbicidal compositions containing substituted, 1,2,4-triazinones and 3-(5-butylsulfonyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea, the compositions taught as being useful for selective postemergence weed control in cereal, potato, tomato and soybean crops. Such use is against terrestrial weels, and there is no teaching which would suggest the use of the 1,3,4-thiadiazol-2-ylurea component of the combination alone as an aquatic herbicide.
The search for an effective aquatic herbicide continues, since there exists a very distinct need for a method of controlling the growth of aquatic weeds.